Free piston internal-combustion gas generator operated at constant compressor clearance volume



Dec. 26, 1950 R. .1. WELSH FREE PISTON INTERNAL-COMBUSTION GAS GENERATOR OPERATED AT CONSTANT COMPRESSOR CLEARANCE VOLUME 3 Sheets-Sheet 1 Filed Oct. 14, 1947 1950 R. J. WELSH 2,535,558

FREE PISTON INTERNAL-COMBUSTION GAS GENERATOR OPERATED AT CONSTANT COMPRESSOR CLEARANCE VOLUME Filed Oct. 14, 1947 3 Sheets-sheet 2 53 I0 5393 D N 1 I! I N m 5 9. o 5 G L u E2 Z is.

Dec. 26, 1950 R. J. WELSH 2,535,558

FREE PISTON INTERNAL-COMBUSTION GAS GENERATOR OPERATED AT CONSTANT COMPRESSOR CLEARANCE VOLUME 5 Shets-Sheet 5 Filed Oct. 14, 1947 Q oE .8 N. MT Q mo. H Etna zacbmnz. i

mm mm t mu I *m w E N a m. 6 8 m m. mm

Patented Dec. 26, 1950 FREE PISTON INTERNAL-COMBUSTION GAS GENERATOR OPERATED AT CONSTANT COMPRESSOR CLEARANCE VOLUME Robert James Welsh, Rugby, England, assignor to The English Electric Company Limited, London, England, a British company Application October 14, 1947, Serial No. 779,799 In Great Britain September 30, 1942 Section 1, Public Law 690, August 8, 1946 Patent expires September 30, 1962 12 Claims.

This invention relates to a free piston internal combustion gas generator, i. e., a device wherein a compressor piston is directly connected to or combined with an internal combustion engine piston and usually also with a suction piston, which device is used to supply a gas turbine, which may have as its working fluid either (I) solely air coming direct from the compressor or (II) solely the exhaust from the engine cylinder (comprising the products of the combustion in the engine cylinder mixed with scavenging air supplied to the engine by the compressor) or (III) a. mixture of the engine exhaust with air coming direct from the compressor. The second of these three alternatives is most usual.

The stroke of the free piston is usually variable, i. e., both the innermost point reached by the piston at the end of the compression of the charge in the engine cylinder (which may be called the inner dead centre) and the outermost point reached by the piston at the end of the combustion stroke (hereinafter called the outer dead centre) vary throughout operation.

The variation in the outer dead centre has hitherto resulted in a corresponding variation in the clearance volume (at the end of the outstroke) in any buffer cylinder and also in the compressor cylinder where compression takes place during the outward stroke.

A free piston internal combustion gas generator according to the present invention operates with a stroke and an outer dead centre position varying with variations in the compressor output, means responsive to the change of load of the gas turbine being however provided for maintaining the clearance space in a compressor cylinder or an associated buffer cylinder (or both) at the end of the outward stroke substantially constant over a range of difierent positions of the outer dead centre. Furthermore, in a gas generator according to the invention, automatic adjustment means are provided for moving one end boundary wall of the clearance space in a compressor or buffer cylinder (or both) towards the other end boundary wall on a decrease in the outward stroke, i. e., for varying the efiective overall length of a cylinder, so as to reduce or substantially eliminate the variation in the said clearance volume or volumes with variation in the outer dead centre position over a range. Preferably, as shown in the accompanying drawings, the boundary wall of a cylinder or cylinders is moved by the said adjustment means so as to increase the cylinder length with an increase in stroke and to decrease this length with a decrease in stroke. Preferably the automatic adjustment means act, upon a change of load on the turbine in anticipation of the consequent change of stroke of the gas generator; thus a change in fuel supply (to alter the output) may be accompanied b appropriate movement of one end boundary wall, or alternatively an alteration of the output may be initiated by moving the end boundary wall, the fuel supply then being controlled in response to any deviation of the clearance volume from the desired value.

Of the accompanying drawings, Fig. 1 shows a longitudinal section through rather more than half the length of a free piston internal combustion gas generator of the opposed piston type embodying the invention, while Fig. 2 shows a cross section through the compressor cylinder on the line 2-2 of Fig. 1. Fig. 3 shows plant incorporating a free piston gas generator as in Figs. 1 and 2 supplying motive fluid to a turbine in conjunction with means for regulating the fuel supply to its internal combustion cylinder and for controlling the clearance volume according to the invention, while Fig. 4 is a modification of Fig. 3 incorporating a different method of control. Fig. 4a is a detail of Fig. 4 on a larger scale. Fig. 4b is another detail of Fig. 4 on a larger scale.

In Figs. 1 and 2 the body of the free piston gas generator comprises the engine cylinder I and the pair of compressor cylinders 2 at opposite ends thereof closed by the cylinder heads 2b. The buffer cylinders 3 form part of the blocking pistons 3a movable in the cylinders 2 towards and away from the compressor pistons 5 to vary the clearance volumes in compressor and buffer cylinders. Each free piston unit consists of one of the opposed engine pistons l reciprocating in cylinder l, a compressor piston 5 reciprocating in one of the cylinders 2 and a butter piston 6 reciprocating in one of the movable buffer cylinders 3. The annular space within the blocking piston 3a around the buffer cylinder 3 is divided into two separate parts by the radial webs 3b (Fig. 2) and partly closed at the back by the back plate 30 (Fig. 1). In the inner dead centre position the piston 6 clears a port Si in the cylinder 3 so as to connect the latter with the lower part of the annular space within the blocking cylinder 3a. In the head of this blocking piston there are one or more suction inlet valves l2 which can open to put the suction inlet 14 in communication with the interior of the cylinder 2 through the openings 2a in the cylinder wall and one part of the interior of the blocking piston 3a through the apertures 3d therein. The guide I! (Fig. 2) keeps the apertures 2a and 3d in alignment. Also in the head of the blocking piston there are one or more discharge valves l3 which can put the cylinder 2 in communication through the other part of the interior of the blocking piston, the apertures Se in a part of the back plate 30 and the conduits l5 with the annular space surrounding the ring of inlet ports la in the engine cylinder 5. The ring of exhaust ports lb in the latter opens into an annular space communicating with the exhaust conduit H6.

The reciprocating piston units can be synchronised in well known and usual manner by being linked by a pair of links such as l to the opposite ends of a lever 8 having its midpoint pivotally supported on the outside part of the engine cylinder Fuel can be injected into the cylinder l by fuel injectors 9 of conventional form supplied through a distributor (not shown) also of conventional form by the fuel injection pump it also of conventional form reciprocated by cam I l which is oscillated (in accordance with the movement of the free piston units) by the lever which is connected by link 2! to a point on one of the links 7. The quantity of fuel injected by each stroke of the pump Ill is determined in the usual manner by the position of the fuel rack Illa.

Each cylinder head 212 carries a servo-motor cylinder 18 within which is slidable a piston l9 connected by piston rod 22 to the rear of the buffer cylinder 3 whereby the latter can be moved to diiferent positions within the compressor cylinder 2.

In Fig. 3 the internal combustion gas generator according to Figs. 1 and 2 is shown connected to supply motive fluid through the exhaust conduit 16 to the gas turbine 23. A speed governor 24 for the turbine, and which is driven thereby through gearing 25 acts through levers 26 and 28 and links 2? and 29 to move the fuel rack hid in order to regulate the fuel supply to the engine cylinder in accordance with the load on the turbine, the fuel supply being increased in response to a decrease in turbine speed and decreased in response to an increas in turbine speed. The governor also sets in motion the fluid pressure servo-motor pistons l9. For this purpose the links 2? turn the lever 39 about its fixed pivot. able in a slotted arm slid of this lever is the slider block 3i on the end of link 32 which acts on levers 33 to move the piston valves 34 in the valve bodies 35 thereby connecting one end of each cylinder 38 to the source of fluid pressure and the e.

other end to the sump thereof. This sets the pistons i9 and the blocking pistons 3a in motion until the clearance volume (at the end of the outstroke) is correctly adjusted,'when the pistons l9 acting through the levers 33 will restore the valves 34 to their normal closed position. The arrangement is such that on a decrease in power output, 1. e., when in response to an increase in the speed of the turbine the governor moves the links 21 downwards and thereby moves the fuel rack Illa in a sense to decrease the quantity of fuel injected per cycle, the blocking pistons move towards the compressor pistons 5 in order to decrease the efiective length of the cylinder 2, thus tending to maintain a more nearl constant clearance volume at the outer end of the stroke of pistons 5 and 6. Conversely, movement of the links 27 and fuel rack Illa in a sense to increase the power output tends to set the blocking pistons 3a. in motion in a sense to increase the effective length of cylinders 2, thereby again tending to maintain the said clearance volume in cylinders 2 and 3 substantially constant.

Since the variation in piston stroke will depend in part on the fuel supply and in part on the dclivery pressure of the compressor, the position to which the pistons 3a are adjusted by the governor 2 3 in accordance with a particular adjustment of the fuel rack lila is varied according to the delivery pressure of the compressor cylinder 2. To this end, the conduit i5 is connected by pipe 36 to a cylinder 3! wherein the pressure acts on a piston 38 against the force of a biassing spring 39 to move the link 32 about its pivotal connection to the lever 33, thereb moving the slider block 3! in the slotted arm 30a of lever 30.

In the modification shown in Fig. 4 the turbine governor 24 is not linked directly to the fuel rack Illa but acts through the levers 2E and links 21' solely on the valves 34 movable through levers 33 in the cylinder to control the supply to the cylinders I8 in which move the servo-motor pistons IQ for moving the blocking pistons So as already described. The fuel supply is controlled in response to any change in the peak pressure in the buffer cylinder 3 at the end of the outward stroke from a predetermined value. To this end, air compressed in one of the buffer cylinders 3 can pass through the non-return valve All (Fig. 4a) into the chamber 20 formed on the cylinder cover 2b through the pipe 41 movable with the blocking piston 3a and slidable through a gland formed in the cylinder cover 2b. This chamber is connected with the cylinder 42 in which is movable the piston 43 against the force of loading spring 44. The clearance volume in the whole space between the back of the valve and the back of the piston 43 including the chamber 20 and the connecting pipes constitutes an air capacity chamber to which air is supplied during the compression stroke of piston 6 in cylinder 3 and from which there is a slight leak off from a calibrated orifice 4211 (Fig. 47)) at the rear of cylinder 42. Thus the pressure in the cylinder .2 acting on the piston d3 against the force of spring 44 is substantially a measure of the peak pressure in the clearance volume in cylinder 3 and hence a measure of the clearance volume at the end of the outstroke. This peak pressure is altered by any change in load on the gas turbine 23 in that a reduction of load will tend to raise the speed of the turbine 23 and this, through the mechanism of the governor 2 links and levers 25, 27, 33 and the servo mechanism [8, i9, 34, causes the blocking pistons 3a to move inwards. One immediate effect of any such inward movement of the blocking pistons 3a will be to raise the peak pressure in the buffer cylinder 3. which increased pressure will, in turn, operate through the pressure responsive device 42, 43, and the servo-motor 45, 46, 41 to effect a reduction in the fuel supply by appropriate movement of the fuel pump control rack Illa.

What I claim as m invention and desire to secure by Letters Patent is:

1. A free piston internal combustion gas generator for supplying motive fluid to a gas turbine and comprising a combustion cylinder, at least one compressor cylinder, at least one engine piston and at least one compressor pis on adapted to reciprocate together as a free piston assembl in the said cylinders at a variable length of stroke depending on th load on said gas turbine, and automatic adjustment means resronsive to the load on the gas turbine and adapted to maintain the clearance volume in the said compressor cylinder substantially constant over a range of outer dead centre positions associated with the said variable length of stroke of the said free piston assembly.

2. A free piston internal combustion gas generator for supplying motive fluid to a gas turbine, and comprising ,a combustion cylinder, a pair of compressor cylinders, a pair of cushion cylinders, a pair of engine pistons, a pair of compressor pistons and a pair of cushion pistons, the said pistons being adapted to reciprocate as pairs of free piston assemblies in-the said cylinders at a variable length of stroke depending on the load on said gas turbine, and automatic adjustment means responsive to the load on the gas turbine and adapted to maintain the clearance volume in at least one of the two pairs of cylinders substantially constant over the range of outer dead centre positions associated with the said variable length of stroke of the said free piston assemblies.

3. A free piston internal combustion gas generator for supplying motive fluid to a gas turbine, and comprising acombustion cylinder, at least one compressor cylinder, at least one engine piston and at least one compressor piston adapted to reciprocate together as a free piston assembly in the said cylinders at a variable length of stroke depending on the load on said gas turbine, a movable end boundary wall at the end of the clearance space of the said compressor cylinder, and automatic adjustment means responsive to the load on the gas turbine, and adapted to move the said boundary wall in a sense to reduce substantially any variations of the said clearance space over a range of outer dead centre positions associated with the said variable length of stroke of the said free piston assembly.

i. A free piston internal combustion gas generator as claimed in claim 3 including a blocking piston on the clearance space side of the compressor cylinder adapted to be moved by the said automatic adjustment means in a sense to increase the effective length of the said compressor cylinder with increasing length of stroke of the free piston assembly.

5. A free piston internal combustion gas generator as claimed in claim 4 including a bufier cylinder carried by the said blocking piston and a buffer piston movable therein and forming part of the free piston assembly.

6. A free piston internal combustion gas generator for supplying motive fluid to a gas turbine, and comprising a combustion cylinder, a pair of compressor cylinders and a pair of cushion cylinders, a pair of engine pistons, a pair of compressor pistons and a pair of cushion pistons adapted to reciprocate as pair of free piston assemblies in the said cylinders at a variable length of stroke depending on the load on said gas turbine, movable end boundary walls at the end of the clearance space of at least one of the said pairs of cylinders, and automatic adjus ment means responsive to the load on said gas turbine, and adapted to move the said boundary walls in a sense to reduce substantial'y any variations of the said clearance spaces over a range of outer dead centre positions associated with the said variable length of stroke of the said free piston assemblies.

7. A free piston internal combustion gas generator for supplying motive fluid to a gas turbine and comprising a combustion cylindenat least one compressor cylinder, at least one cushion cylinderyat least one engine piston, at least one compressor pistonand at least one cushion piston adapted to reciprocate togetheras a free piston assembly in the said cylinders at a variable length of stroke depending on the load on said gas turbine, a movable end boundary wall at the end of the clearance space of the said compressor cylinder and cushion cylinder, means for regulating the fuel supply to the said engine cylinder, and automatic adjustment means responsive to the load on the gas turbine and to the peak pressure in the clearance volume of the said cushion cylinderat the end of the combustion stroke of the said free piston assembly arranged for controlling both the said fuel supply regulating means and the said boundary walls so as to move the latter outward with the fuel supply increasing, and inward with the fuel supply decreasing in order to meet the variations in the length of stroke of the free piston assembly consequent to such variation in fuel supply.

8. A free piston internal combustion gas generator for supplying motive fluid to a gas turbine and comprising a combustion cylinder, at least one compressor cylinder, at least one cushion cylinder, at least one engine piston, at least one compressor piston and at least one cushion piston adapted to reciprocate together as a free piston assembly in the said cylinders at a variable length of stroke depending on the load on said gas turbine, a movable end boundary wall at the end of the clearance space of the said compressor cylinder and cushion cylinder, means for regulating the fuel supply to the said engine cylinder, and automatic adjustment means comprising a speed governor driven by said gas turbine and mechanically linked to said boundary wall and said means for regulating the fuel supply, a pressure cylinder connected to the compressor delivery, a piston in said pressure cylinder responsive to pressure variations therein and linked to the said speed governor such that an increase: in said pressure, corresponding to a decrease in turbine speed or increase in turbine load, reduces the movement of the said movable wall in an outward sense and that a decrease in said pressure, corresponding to an increase in turbine speed or decrease in turbine load, increases the movement of the said movable wall in an outward. sense.

9. A free piston internal combustion gas generator for supplying motive fluid to a gas turbine and as claimed in claim 3 including adjustment means responsive to the peak pressure in the clearance volume of the cushion cylinder at the end of the combustion stroke of the said free piston assembly, and means for regulating the fuel supply to the said engine cylinders controlled by the said responsive means in a sense of increasing the fuel supply with increasing clearance volume, and reducing the fuel supply with decreasing clearance Volume.

10. A free piston internal combustion gas generator for supplying motive fluid to a gas turbine and as claimed in claim 9 including an air chamber, a non-return valve adapted to establish communication from the said clearance space to the said air chamber, a leak from the said chamber adapted to maintain the pressure inside said chamber substantially proportional to the maximum pressure in said clearance space, a fluid pressure servo-motor adapted to actuate the said fuel supply regulating means, and a control va ve governed by the pressure in said air chamber adapted to apply fluid pressure to the said servomotor in the sense of increasing the fuel supply with decreasing air pressure, and of reducing the fuel supply with increasing air pressure.

11. A power plant comprising a free piston internal combustion gas generator as claimed in claim 3, a gas turbine in supply connection with 5 the gas delivery side of the said compressor, a speed governor actuated by the said turbine, and a control connection between the said speed governor and the said movable wall in a sense of moving the said walls inwards upon an increase 10 of speed and outward upon a reduction of Speed.

12'. A power plant as claimed in claim 11 including a fluid-pressur servo-motor adapted to move the said movable wall, and a control valve for said servo-motor controlled by the said speed governor in a sense of moving the said movable Wall inwards upon an increase of speed and outward upon a reduction of speed.

ROBERT JAMES WELSH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Janicke July 6, 1937 Number 

